Adding the unique prefix option

This solves a few problems with the unique jobs

1. Ability to delete all the unique payloads in a snap, without the jobs
actually being performed. For example when you delete an entire queue
for some reasons, you would like it to get queued up again.

2. Obscure keys for the unique payloads, this way you can better
uidentify it.

Also refactored the payloads a bit, cleaned up etc..
Merge pull request #8 from KensoDev/feature/unique_job_prefix

Adding the unique prefix option